In case a workpiece is to be machined by a machine tool, for example, loads accompanying the machining in various directions are generally exerted between the machine tool and the workpiece, although depending upon the kinds of machining such as cutting or polishing, the material of the workpiece or the machining conditions. The loads act as reaction forces upon the machine tool and the workpiece. If the machine tool and the workpiece are completely fixed at the instant of machining against the loads, the machining can be ideally accomplished in a drastically improved precision.
In the case of machining of the workpiece using such machine tool, one of the machine tool or the workpiece is fixed whereas the other is moved by means of a mechanism such as a linear sliding bearing.
The linear sliding bearing known to used for this purpose is constructed to include: a track base having axial races; a sliding bed having endless tracks which are formed of load regions having load races facing the races of the track base and no-load regions providing the communicating connections between the two ends of the load regions; and rollers circulating in the endless tracks for bearing the loads between the races of the track base and the load races of the sliding bed. Thus, the linear sliding bearing can bear the loads in the four directions, i.e., radial, inversely radial and rightward and leftward directions. In the linear sliding bearing of this kind, moreover, the rigidities in the four directions are enhanced by applying a prepressure to the rollers to bear the four-directional loads to be generated between the machine tool and the workpiece during the machining, so that the accompanying chatter marks and vibrations may be suppressed as much as possible to improve the machining precision. In connection with the axial direction of the track base, on the other hand, frictions in the movements are suppressed with a view to lightening the loads upon the feeding drive system such as a feeder of screw and nut type or a motor mechanism. The rigidity necessary for the machining in the axial direction of the track base relies exclusively upon that of the feeding drive system.
Incidentally, the rigidity of the feeding drive system is determined, if the system is the feeder of screw and nut type, by the rigidity of the feed screw or nut itself, the rigidity of the support of the feed screw or nut, and the rigidity of the motor for applying a rotating force to the feed screw. In order to increase the rigidity of the feeding drive system, it is necessary to enlarge the size of the feed screw or nut or to raise the output of the motor. Thus, the increase in the rigidity of the feeding drive system is intrinsically limited by the problems which are caused by increasing the size of the apparatus or by raising the cost for the feeding drive system.
As various products are required to be the more precise in the industry of recent years, a machine apparatus such as the machine tool for machining the products is required to have its machining precision improved the better. Thus, the linear sliding bearing taking a leading role for the machining precision of the various machine apparatus is requested to improve the machining precision.
It is, therefore, an object of the present invention to provide a linear sliding bearing which can have not only the rigidities of four directions, i.e., the radial, inversely radial, rightward and leftward directions but also a predetermined rigidity in the axial direction of the track base.
Another object of the present invention is to provide a linear sliding bearing which can apply the rigidity in the axial direction of the track base, if necessary, and adjust the level of the rigidity.
Still another object of the present invention is to provide a linear sliding table which can mount a machine apparatus such as a machine tool for machining of high precision.